1. Field of the Invention
The present invention relates to an apparatus for monitoring tuned harmonic filters, the apparatus being capable of disconnecting a filter from an electrical system to prevent damage to either the electrical system or the filter components. More particularly, the present invention comprises a monitor apparatus which is operatively connected to a filter device providing "clean" power to an electrical system. The monitor is adapted to compare the actual operating conditions of the filter with the preferred operating conditions of the filter and disconnect the filter and/or the electrical system when the monitor detects dangerous operating conditions.
A tuned harmonic filter is adapted to remove distortion caused by non-linear loads and protect sensitive equipment from damaging resonance conditions. Such a filter is designed to protect against motor cogging and damage, overheating transformers and wires, flickering lights, computer data loss, power capacitor failure, and power factor penalties. Since the consequences of the failure of such a filter may result in high repair costs, it is highly desirable to verify that the filter is operating within its designed parameters. The monitoring apparatus of the present invention is designed to monitor the operation of a filter and remove the filter and/or the electrical system from "on-line" if or when the filter does not meet its operating parameters, thus preventing damage to the filter and the electrical system.
2. Description of the Relevant Art
There are known devices which can be used to detect malfunctions or defects of electrical devices. Such previous devices have various shortcomings which the monitor apparatus of the present invention overcome.
U.S. Pat. No. 4,972,153 discloses an apparatus for detecting malfunctions in a group of electrical devices. The apparatus employs a current transformer for measuring energy levels in the electrical devices. However, a true indication of the power dissipation in a filter reactor is not taught by this device.
U.S. Pat. No. 4,845,435 discloses a sensor fault detector which utilizes a reference voltage and a plurality of comparators to produce a signal representative of properly operating sensors. However, this detector relies solely on voltage to indicate failure of the sensors.
U.S. Pat. No. 4,142,151 discloses a fault detector for diodes in an array of parallel diodes comprising heat-sensitive material that changes appearance when its temperature is raised. A resistor is situated such that it generates heat when a diode fails, causing the material to change color indicating a fault.
U.S. Pat. No. 3,200,392 discloses a circuit for counting the number of rectifier cell failures. Once a present number of failures is reached, the system is automatically shut off. A voltage pulse is generated each time there is a cell failure.
The above-discussed devices and other known monitoring instruments have various problems and shortcomings. These devices have failed to provide a monitoring apparatus associated with a harmonic filter including indicating means and means for removing the filter and its associated electrical system from "on-line" status.